Vourc'h 2020.

Study characteristics
Methods	RCT, parallel‐group design. Single‐centre study
Participants	Total number of randomized participants: 98 Setting: ICU; France Inclusion criteria: ≥ 18 years of age; admitted to the ICU after CABG presenting with severe hypoxaemia after extubation Exclusion criteria: pregnancy; chronic respiratory failure; combined cardiac surgery; alteration of consciousness or requiring immediate intubation; surgical complications requiring re‐operation; haemodynamic instability or ventricular arrhythmia; adults subject to legal protection; already participating in an interventional study on oxygenation Baseline characteristics: Intervention group (HFNC): Age, mean (SD): 67.6 (± 9.4) years Gender, M/F: 36/7 BMI, mean (SD): 28.7 (± 3.8) kg/m2 SAPS II, mean (SD): 26.9 (± 9.4) PaCO2, mean (SD): 39.8 (± 4.5) mmHg PaO2/FiO2, mean (SD): 131.5 (± 27.7) mmHg Control group: Age, mean (SD): 65.8 (± 10.1) years Gender, M/F: 41/8 BMI, mean (SD): 29.7 (4.5) kg/m2 SAPS II, mean (SD): 26.4 (± 6.0) PaCO2, mean (SD): 40.5 (± 3.8) mmHg PaO2/FiO2, mean (SD): 147.7 (± 30.7) mmHg
Interventions	Intervention group (HFNC): Randomized, n = 49; losses, n = 8 (2 withdrew consent; 6 not included in per protocol analysis: 1 without severe hypoxaemia, 4 received control group therapy, 1 intubation before day 1); analysed, n = 47 in ITT; 41 in per protocol Details: after extubation, HFNC via Optiflow, with gas flow rate of 45 L/min, FiO2 of 100% and adjusted according to the SpO2, and temperature of 37 ºC. Device was switched every 6 hours to a Venturi mask to avoid hyperoxia. Control group: Randomized, n = 49; losses, n = 8 (6 withdrew consent; 2 not included in per protocol analysis: 1 without severe hypoxaemia; 1 received intervention group therapy); analysed, n = 43 in ITT, 41 in per protocol Details: non‐rebreather facemask (Hudson RCI) with humidified oxygen, gas flow rate of 15 L/min, with FiO2 of 100% and adjusted according to the SpO2. No CPAP valve on the face mask. Device was switched every 6 hours to a Venturi mask to avoid hyperoxia.
Outcomes	PaO2/FiO2 (1, 6, 24 and 48 hours); PACO2, respiratory rate and heart rate at 48 hours; treatment failure defined as SpO2 < 96% despite treatment or respiratory rate ≥ 25 breaths/min; need for NIV or reintubation for treatment failure; increased work of breathing, or hypercapnia; tolerance of the device (satisfaction; occurrence of nasal bleeding; mucus dryness during therapy); radiologic score on chest X‐ray; mortality; length of stay in the ICU Note: data were available as ITT and per protocol. We used the ITT data because these data were clearly reported by study authors.
Notes	Funding/declarations of interest: source of funding (a grant for research and innovation missions) was not specified. However, funding was allocated to the university sponsor and Fischer & Paykel; Fischer & Paykel did not participate in study design, conduct, data management or interpretation of the results. Individual authors declared personal fees and funding from LFB, Fischer & Paykel, Baxter, MSD, and Pfizer for other work. Study dates: June 2011 to April 2015
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated randomization
Allocation concealment (selection bias)	Low risk	Randomization controlled by an independent research unit, allocation provided via opaque envelopes
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Blinding was not possible. Although we expected that this would not influence outcome data, we could not be certain of this.
Blinding of outcome assessors (objective outcomes)	Low risk	Blinding of outcome assessors was not described; we did not anticipate that this would influence the assessment of objective outcome measures.
Blinding of outcome assessors (subjective measures)	Low risk	Study was described as open‐label, and we assumed that participants were aware of their group allocation. We did not think that lack of blinding would influence participants' assessment of subjective measures.
Incomplete outcome data (attrition bias) All outcomes	Low risk	We noted losses in each group, however, these were clearly reported and reasonably balanced and we did not expect the losses to cause risk of attrition bias.
Selective reporting (reporting bias)	Unclear risk	Registration with a clinical trials register, or a prepublished protocol was not reported. It was not feasible to effectively assess risk of selective reporting bias without these reports.
Other bias	Low risk	We identified no other sources of bias.